A notebook PC generally includes a main body portion that houses a processor, motherboard, associated peripheral components, rechargeable batteries, disk drives, cursor controls and a keyboard, and a display portion that is pivotably joined to the main body. The display of a notebook PC typically is joined to the main body by a pair of spaced, single-axis hinges positioned on a common horizontal axis at or near a back edge of the main body. The hinges enable the display to pivot in clamshell fashion from a closed position in which the display is folded face down over the keyboard and secured in place, through a range of working positions in which the display faces the keyboard, to a fully open position in which the display can lie in a face up, 180 degree position next to the main body, or, in some examples, can be pivoted beyond 180 degrees to a position behind the main body.
A tablet PC is modeled after an ordinary pen and pad of paper and integrates a sensor array, which generates signals according to where it has been touched, such as by a specialized digital stylus, together with a flat panel display to form a digital writing tablet. The display screen/writing tablet essentially covers the entire top surface of the main body of the tablet PC where traditional keyboard and cursor controls are located on a notebook PC. With a suitable handwriting recognition software platform, users can interact with the tablet PC and input a wide variety of data including text and graphics, simply by writing on the display surface with the digital stylus or pen. Although the tablet PC represents a significant advance, many users find that a keyboard is still necessary for some applications. Thus, a hybrid or convertible notebook/tablet PC has been developed that enables a tablet PC to be converted back and forth between a notebook mode in which the display faces the keyboard and a tablet mode in which the display/writing slate overlies the keyboard.
A variety of hybrid notebook/tablet PCs mount the display to the main body on joint or hinge assemblies that enable the display to be maneuvered from a notebook to a writing tablet mode without being detached or disconnected electrically. For example, the display of a notebook/tablet hybrid PC can be mounted to the main body on a single multiaxial hinge assembly positioned at or near the center of a back edge of the main body. Such a multiaxial hinge assembly enables the display to be pivoted open and closed about a pivot axis in a manner similar to the typical notebook PC described above, and also enables the display to be rotated about a second “center” or vertical axis that is orthogonal to the pivot axis. Rotation about the center or vertical axis allows the display to be oriented facing toward or away from the keyboard side of the PC at a variety of angles. When the display is rotated 180 degrees to face away from the keyboard, it can then be closed face up over the keyboard to provide a writing tablet. When the display is rotated back to face the keyboard the PC can be used as a notebook and the display can be closed face down to cover the keyboard and display for storage.
While a number of different hinge and joint assemblies can be employed to mount the display of a hybrid notebook/tablet PC, such as universal joints, saddle joints, ball and socket joints, and the like, essentially, any such hinge or joint assembly will have at least two orthogonal axes of rotation and provide sufficient rotational freedom thereabout to convert the hybrid tablet/notebook PC between notebook and tablet modes. Such a mechanism, referred to herein as a multiaxial hinge assembly, is a hinge or joint assembly that enables rotation about at least two orthogonal axes (i.e., axes that are mutually perpendicular).
Although a hybrid notebook/tablet PC with a multiaxial hinge that limits rotation about the center axis to 180 degrees can easily be converted between notebook and tablet modes, unfortunately, it is often difficult for users to remember which way the display must be rotated to change from one mode to another. The hinge mechanism does not provide any external indication of the correct direction of rotation and often provides inadequate sensory feedback when an incorrect rotation is attempted. For example, a hinge stop mechanism may prevent rotation of the hinge beyond its predetermined limits but the flexibility inherent in a portable PC display panel, which will act as a lever against the hinge, makes it difficult for users to sense that the hinge is at a rotational limit, particularly so if torque detents are also used to help hold the display in place at 0 and 180 degrees. Considerable torque can be applied to the hinge in the wrong direction before the user senses the hinge is against a stop, rather than a detent (soft) stop. Repeated attempts to rotate the hinge against the stop mechanism may cause the hinge or stop to loosen up, rendering it even more difficult to determine when the hinge is at the limit. Excessive play in the stop mechanism may also cause failure of the latch that secures the display to the main body and which depends on the hinge stop mechanism for proper alignment. Thus, there is a need for a hybrid notebook/tablet multiaxial hinge assembly that provides a reliable, easy to interpret indication to a user of the correct direction to rotate the display to reduce the likelihood of damage to the hinge assembly and/or display from attempts to rotate the hinge beyond a rotational limit.